The present invention relates to an aerosol type, non-barrier, spray can for materials in fluid or liquid form and particularly relates to an especially thin walled aerosol spray can.
Many fluent materials and particularly liquid materials are dispensed from pressurized aerosol spray cans of the non-barrier type, wherein there is no separation between the fluent material to be dispensed and the can pressurizing propellent. The present invention is primarily directed to a non-barrier can. A barrier can has a moveable barrier in it, such as a piston or an enlarged or flexible diaphragm, where the material to be dispensed is at the side of the barrier toward the outlet from the can and the propellant is on the other side of the barrier and pushes against the barrier and pushes the fluent material through the can outlet. The propellant typically is not expelled along with the product. Barrier cans are primarily designed for handling viscous products, because a non-barrier can will not be able to dispense these products.
The aerosol spray can of the invention has a spray forming and dispensing valve on it with a small flow orifice which communicates between the interior of the can and a small swirl chamber in the spray dispensing button. The mixed fluent material and propellant enter the swirl chamber in the spray button and from there exit the spray button through a spray outlet. When the valve is opened, the elevated pressure in the can forces a mixture of the propellant and the fluent material through the valve orifice into the swirl chamber. The rapid drop to ambient pressure as the swirling mixed propellant and fluent material exit the orifice of the button into the surrounding atmosphere, sometimes coupled with the flashing off into gaseous form of some still liquid propellant, and coupled with the rapid expansion of the compressed propellant as it exits the valve orifice, atomizes the fluent material and breaks it into small droplets. This breakup is sometimes aided by propellant vapor which flows from the can through an additional vapor tap into the valve chamber which increases the amount of propellant available to force the spray mixture out of the button exit spray orifice. If a stream or foam is desired, a modified valve having no swirl chamber and a large orifice is used.
Objectives for such cans include being able to expel essentially all of the fluent material from the can and for the character of the spray, stream or foam to remain as uniform as possible throughout the entire contents of the can.
The conventional ways to accomplish these objectives have been, in the case of compressed gases, to use the initial pressures of about 90-140 psig or 621-965 kPa and, in the case of liquified gases, to use sufficiently large amounts of the liquified gas. In the case of liquified gas, the pressures of 70.degree. F. or 21.degree. C. may only be about 30-50 psig or 207-345 kPa. These pressures, however, rise to much higher values at higher temperatures due to the temperature/pressure relation of liquified gases. The increased pressure in the can has required that the can wall be made relatively thick so that the can does not permanently distort or rupture from the high pressure encountered during can filling, storage, transportation and use. During some of the storage and transportation stages, cans are exposed to elevated ambient temperatures, so that the can must be able to withstand the elevated gas pressures caused by elevated temperatures.
Several government agencies have mandated that certain types of aerosol cans have particular strengths or distortion and burst resistances for safety. This is to prevent can distortion and the danger which accompanies the bursting of a pressurized aerosol can. For example, the United States Department of Transportation (DOT) has a regulation that for sealed cans having less than 27.7 fluid ounce or 819.2 cc capacity, the can must be able to withstand and not permanently distort at an internal pressure equal to the equilibrium pressure of its intended contents, including fluent material and propellant at 130.degree. F. or 54.4.degree. C., and that the pressure in the can must not exceed 140 psig or 965 kPa at 130.degree. F. or 54.4.degree. C. If the pressure in the can exceeds 140 psig or 965 kPa, then there are special specifications for that can. The DOT requires that there be no permanent distortion of the can at 130.degree. F. or 54.4.degree. C. and that the same can not burst at a pressure that is one and one-half times as great as the pressure at 130.degree. F. or 54.4.degree. C. For example, if the equilibrium pressure in the can at 130.degree. F. or 54.4.degree. C. is 140 psig or 965 kPa, then the can should not burst at 210 psig or 1448 kPa.
Aerosol spray cans for spraying fluent materials use various liquified and compressed gas propellants. Liquified propellants have included chlorofluorocarbons, some sold under the trademark "Freon", some of which are no longer permitted for use as a spray can propellant except for use with certain pharmaceuticals, or hydrocarbons, or dimethylether and other volatile liquids. Compressed gas propellants have included carbon dioxide, nitrous oxide, nitrogen, air, etc. Liquid propellants have a benefit over compressed gases because just enough liquid evaporates to maintain relatively constant gas pressure in the can and the remaining liquid provides a reservoir for producing more gas as propellant is expelled. With compressed gas propellants, in contrast, enough gaseous propellant must be initially placed in the can to be able to spray out or otherwise dispense the entire contents of the can at sufficient pressure.
In order for aerosol dispenser cans to withstand the expected elevated internal pressures and to meet DOT standards, known cans have been made of metal, i.e. steel or aluminum, with a great enough wall thickness. For a typical steel can of 2 1/16 inch or 52.4 mm in diameter to safely contain pressurized contents at 140 psig or 965 kPa, that is, a can not made for containing extra high pressures, the wall thickness has been about 0.008 to 0.012 inch or 0.020 mm to 0.304 mm. The bottom and top of the can, which will normally bulge and distort outward under too much pressure, have had a thickness in the range of 0.012 to 0.018 inches or 0.304 to 0.457 mm. With the above noted can wall and top and bottom thicknesses, a steel can 5 9/16 inches or 14.13 cm high might have a weight of 59 grams. For an aluminum can of the same dimensions to be able to withstand the pressures indicated, it would have a wall thickness of about 0.012 inches or 0.304 mm and a bottom thickness of about 0.016 inches or 0.406 mm. These steel and aluminum cans are thick walled enough to be rigid and not deformed under normal finger force of about 5-10 lbs or 2.27-4.55 kilograms both when they are filled and pressurized and when they are empty, and they will stay rigid and will not collapse under a vacuum of about 24 inches or 60 cm of mercury. This vacuum is usually used during valve crimping to remove residual air.
Both the steel and the aluminum aerosol spray cans used now have certain drawbacks due to heightened concerns about environmental degradation. It is desirable to reduce the amount of metal used in a can to ease the later disposal burden and because the ores and minerals used in producing cans are in diminishing supply. In addition, more energy is consumed in obtaining the metal ore, in producing the metal and in manufacturing thicker walled cans than thinner walled cans. The cost of transporting the metal of the cans at every stage from initial ore production, through transporting the metal for making the cans to transporting the filled cans is also to be considered. Because billions of pressurized aerosol cans are produced and used each year, a reduction in the wall thicknesses of aerosol spray cans will rapidly have considerable environmental benefit.
Use of lighter weight, thin walled cans as containers for fluent materials is known. For example, for carbonated beverages and some foods, there has been a change from thicker walled, heavier steel cans to lighter, thin walled aluminum and steel cans. In the case of sparkling beverages, the dissolved gas, such as carbon dioxide, and in the case of non-gaseous food, where a gas is added to the can, e.g. liquid nitrogen or compressed air, the added gas pressure gives the soft walled cans rigidity for handling, so that the cans will not be crushed or deformed by normal finger pressure before they are opened. Such soft walled cans, however, have not been used to dispense their contents under pressure. The cans do not have a valve or other outlet system for dispensing their contents which are under pressure. The cans are initially sealed closed. When they are opened, the container pressure immediately goes to atmospheric and the cans lose their rigidity.